This invention relates to a shift assisting device and more particularly to an improved, compact shift assisting device for a transmission such as a marine propulsion transmission.
Many forms of transmissions employ dog clutching elements that are moved into engagement with driving or driven members so as to effect a driving connection. For example, such transmissions are frequently used in the forward neutral reverse transmissions of marine propulsion units and such an arrangement is shown in FIG. 1.
Referring specifically to FIG. 1, there is depicted an input shaft 11 that is coupled in a suitable manner to a prime mover such as a remotely positioned internal combustion engine and which has affixed to its lower end a bevel gear 12 of a forward neutral reverse transmission, indicated generally by the reference numeral 13. The driving gear 12 is enmeshed with a pair of diametrically opposed counter rotating driven bevel gears 14 and 15 that are journaled in a suitable manner on a propeller shaft 16 for driving a propeller (not shown).
A dog clutching sleeve 17 has a splined connection to the propeller shaft 16 and oppositely facing dog clutching teeth that are adapted to be slid into engagement with corresponding dog clutching teeth 18 and 19 formed integrally with the gears 14 and 15 respectively. When the dog clutching sleeve 17 is in a neutral position, the gears 14 and 15 will idle on the shaft 16 and there will be no drive transmitted from the driving shaft 11 to the propeller shaft 16. However, when the dog clutching sleeve 17 engages the gear 14 the shaft 16 will be driven in a forward direction and when the dog clutching sleeve 17 engages the gear 15, as shown in FIG. 1, the propeller shaft 16 will be driven in a reverse direction.
The control of the dog clutching sleeve is accomplished by means of a remotely positioned shift lever 21 that is connected to the dog clutching sleeve 17 by a motion transmitting mechanism including a shift assisting device indicated generally by the reference numeral 22. The motion transmitting mechanism includes an input Bowden wire actuator 23 that is connected at one end to the shift lever 21 and at its opposite end to one end of a lever 24 that is pivotally supported on a plate 25 of the shift assisting mechanism 22. A second Bowden wire actuator 26 is connected at one end to the lever 24 and at the other end to a bell crank 27 which is operative, upon its pivotal movement, to effect movement of the dog clutching sleeve 17 and the afore noted shifting operation.
The shift assisting mechanism 22 includes a lever 28 that is pivotally supported on the plate 25 and has one of its ends affixed to one end of a protective sheath 29 of the Bowden wire actuator 26. When there is a resistance to shifting, the protective sheath 29 will shift in position and pivot the lever 28. This will actuate a proximity switch 31 which then send out a control signal to a shift assisting device. Such shift assisting devices conventionally slow the speed of the powering prime mover that drives the drive shaft 11 so as to relieve the transmission 13 from excess load and facilitate shifting. This may be done in a variety of manners such as by interrupting the ignition, or slowing the engine by closing a throttle valve or similar methods.
The disadvantage of the type of prior art construction as shown in FIG. 1 is that it is relatively complex and requires a number of different connections which may have to be adjusted. That is, the connection of the wire actuators 23 and 26 to the lever 24 and the relationship of the Bowden wire sheath 29 to the lever 28 are all critical. In addition, it should be readily apparent, the construction is somewhat bulky.
It is, therefore, an object of this invention to provide an improved shift assisting device for a transmission.
It is a further object of this invention to provide an improved, compact and highly reliable shift assisting device for a transmission such as a marine transmission.